MySQL: GROUP BY within ranges - php

Question

I have a table with scores like this:
score | user
-------------------
2 | Mark
4 | Alex
3 | John
2 | Elliot
10 | Joe
5 | Dude
The table is gigantic in reality and the real scores goes from 1 to 25.
I need this:
range | counts
-------------------
1-2 | 2
3-4 | 2
5-6 | 1
7-8 | 0
9-10 | 1
I've found some MySQL solutions but they seemed to be pretty complex some of them even suggested UNION but performance is very important. As mentioned, the table is huge.
So I thought why don't you simply have a query like this:
SELECT COUNT(*) as counts FROM score_table GROUP BY score
I get this:
score | counts
-------------------
1 | 0
2 | 2
3 | 1
4 | 1
5 | 1
6 | 0
7 | 0
8 | 0
9 | 0
10 | 1
And then with PHP, sum the count of scores of the specific ranges?
Is this even worse for performance or is there a simple solution that I am missing?
Or you could probaly even make a JavaScript solution...

Answer 1

Your solution:
SELECT score, COUNT(*) as counts
FROM score_table
GROUP BY score
ORDER BY score;
However, this will not returns values of 0 for count. Assuming you have examples for all scores, then the full list of scores is not an issue. You just won't get counts of zero.
You can do what you want with something like:
select (case when score between 1 and 2 then '1-2'
when score between 3 and 4 then '3-4'
. . .
end) as scorerange, count(*) as count
from score_table
group by scorerange
order by min(score);
There is no reason to do additional processing in php. This type of query is quite typical for SQL.
EDIT:
According to the MySQL documentation, you can use a column alias in the group by. Here is the exact quote:
An alias can be used in a query select list to give a column a
different name. You can use the alias in GROUP BY, ORDER BY, or HAVING
clauses to refer to the column:

Answer 2

SELECT
SUM(
CASE
WHEN score between 1 and 2
THEN ...

Answer 3

Honestly, I can't tell you if this is faster than passing "SELECT COUNT(*) as counts FROM score_table GROUP BY score" into PHP and letting PHP handle it...but it add a level of flexibility to your setup. Create a three column table as 'group_ID', 'score','range'. insert values into it to get your groupings right
1,1,1-2
1,2,1-2
1,3,3-4
1,4,3-4
etc...
Join to it on score, group by range. THe addition of the 'group_ID' allows you to set groups...maybe have group 1 break it into groups of two, and let a group_ID = 2 be a 5 set range (or whatever you might want).
I find the table use like this is decently fast, requires little code changing, and can readily be added to if you require additional groupings or if the groupings change (if you do the groupings in code, the entire case section needs to be redone to change the groupings slightly).

Answer 4

How about this:
select concat((score + (1 * (score mod 2)))-1,'-',(score + (1 * (score mod 2)))) as score, count(*) from TBL1 group by (score + (1 * (score mod 2)))
You can see it working in this fiddle: http://sqlfiddle.com/#!2/215839/6
For the input
score | user
-------------------
2 | Mark
4 | Alex
3 | John
2 | Elliot
10 | Joe
5 | Dude
It generates this:
range | counts
-------------------
1-2 | 2
3-4 | 2
5-6 | 1
9-10 | 1

Answer 5

If you want a simple solution which is very powerful, add an extra field within your table and put a value in it for the score so 1 and 2 have the value 1, 3 and 4 has 2. With that you can group by that value. Only by inserting the score you've to add an extra field. So your table looks like this:
score | user | range
--------------------------
2 | Mark | 1
4 | Alex | 2
3 | John | 2
2 | Elliot | 1
10 | Joe | 5
5 | Dude | 3
Now you can do:
select count(score),range from table group by range;
This is always faster if you've an application where selecting has prior.
By inserting do this:
$scoreRange = 2;
$range = ceil($score/$scoreRange);